Developing neurons require trophic factors for survival, growth and differentiation. Nerve growth factor (NGF) was first discovered as a neurotrophic factor that supports the development and maintenance of peripheral sympathetic and neural crest-derived sensory neurons. NGF is a member of a family of proteins that includes brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and NT-4/5. Despite the high sequence homology, the developmental and physiological functions of each factor appear to be different.
Three receptors for the neurotrophic factors of the NGF family are known, and they also form a gene family encoding protein tyrosine kinases. TRK-A encodes a receptor for NGF but also binds NT-3 and NT-4/5. TRK-B encodes a receptor for BDNF but also binds NT-3 and NT-4/5. TRK-C encodes a receptor for Nt-3.
TRK-B has two isoforms, a full length version which has an intracellular domain encoded by the 3' portion of the gene sequence and a truncated version which has essentially no intracellular domain. The intracellular domain of the full length TRK-B is responsible for the receptor's tyrosine kinase activity which is linked to BDNF binding to the receptor. The truncated version, lacking an intracellular domain, does not possess tyrosine kinase activity. The amino acid and nucleotide sequences of rat and mouse TRK-B are known. The amino acid and nucleotide sequences of human truncated TRK-B are known while those of the full length version are heretofore unknown.
There is considerable interest in the role of the TRK family of neurotrophin receptors in regulating growth and differentiation in normal and neoplastic nerve cells. A neuroblastoma is a common pediatric tumor derived from the neural crest. It has been observed that neuroblastoma cells expressing TRK-A can differentiate in response to NGF in culture. The most favorable clinical outcomes are found in patients suffering from neuroblastomas that express high levels of TRK-A transcripts. In contrast, aggressive neuroblastomas, especially those with N-myc amplification, express little or no detectable TRK-A mRNA, and many cell lines have a defective NGF receptor signaling pathway. Little is known about the expression or function of TRK-B in these tumors. TRK-B encodes a tyrosine kinase that binds to brain-derived neurotrophic factor (BDNF), as well as neurotrophin-3 (NT-3) and NT-4/5. These results suggest that the biology of neuroblastomas is closely correlated with the developmental stages of the neurons from which the tumors originate, so neuroblastomas may be regulated in part by neurotrophic factors.
In view of the observation that some neuroblastomas present favorable outcomes in response to therapeutic intervention while others are more aggressive behavior and associated with less favorable prognoses and poor outcomes, it is clinically important to distinguish aggressive forms of neuroblastoma from other, less aggressive neuroblastomas. The course of action to be taken in a patient exhibiting neuroblastoma is in part dependent on whether the neuroblastoma is an aggressive form or not because aggressive forms require a more aggressive treatment regimen. Patients suffering from aggressive neuroblastomas must be treated with a relatively potent and specific chemotherapy regimen and surgery may be more appropriate than in those with the type associated with more favorable outcomes. Because the determination of whether a tumor is aggressive or not suggests the prognosis and what course of treatment is warranted, it is crucial to be able to identify whether or not a tumor is an aggressive neuroblastoma in a fast, efficient and reliable manner.
Currently, neuroblastoma may be tested to determine whether or not it possess amplified levels of N-myc. Amplified levels of N-myc indicate an aggressive form of neuroblastoma. The levels of N-myc are evaluated as an indication of aggressive neuroblastoma.
There remains a need for methods of screening neuroblastoma for indications of whether or not it is an aggressive form. Such a method may be used as an alternative to or in concert with the current test to detect levels of N-myc. There remains a need for methods of screening neuroblastoma for indications of whether or not it is an aggressive form by detecting the presence or absence of a marker or target without the need to quantify or determine relative amounts present.
There is a need for the amino acid and nucleotide sequences of human full length TRK-B. The is a need for isolated nucleic acid molecules that encode human full length TRK-B which can be used to transform cells that can then express the human full length TRK-B. There is a need for probes and primers which hybridize to portion of the nucleotide sequences of nucleic acid molecules that encode the human full length TRK-B but not the truncated form. There is a need for antibodies that specifically bind to an epitope on the intracellular domain of human full length TRK-B that is not present in the truncated form.